Lubricating systems for regenerative vacuum pumps

ABSTRACT

In a vacuum pump of the regenerative type or including a regenerative section in which a rotatable substantially vertical shaft is supported by upper and lower bearings, a lubricating system for lubricating the bearings comprising an axial bore extending along the shaft and in communication with radial holes aligned respectively with the lower bearing and the upper bearing, the lower open end of the axial bore extending in to a shaft reservoir containing lubricating fluid, and in which the radial holes in alignment with the lower bearing are formed in a tapered surface of the axial bore.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of patent application Ser. No. 10/164,795 filed Jun. 7, 2002, to be abandoned.

BACKGROUND OF THE INVENTION

This invention relates to vacuum pumps of the regenerative type or vacuum pumps that incorporate a regenerative section and a high speed rotatable vertical shaft supported by bearings at each end of the shaft. In particular, the invention relates to lubricating systems for such bearings.

In vacuum pumps of the regenerative type, a rotor is mounted on a vertical shaft for rotation within a surrounding stator. The shaft is supported by upper and lower bearings that require lubrication. To facilitate lubrication of the bearings the shaft is provided with a central axial bore which communicates with radial holes in alignment with or in the proximity of the upper and lower bearings for delivering a lubricating fluid to the bearings.

It is known to utilize centrifugal force generated by the rotating shaft to draw the lubricating fluid from a reservoir up the axial bore in the form of a thin film to reach the radial holes in alignment with initially the lower bearing and potentially the upper bearing. The lubricating fluid establishes its own conical taper in a straight axial bore provided that a small ledge is available at the lower end of the axial bore. As a single droplet of oil is thrown onto the internal surface of the straight axial bore, the droplet will pass down the surface under the influence of gravity and accumulate at the ledge. When the shaft is rotated rapidly the droplet will experience a significant horizontal component of force that drives the droplet around the inner surface of the bore. However large this force becomes, the gravitational component will continue to influence the droplet such that it ultimately accumulates at the ledge thus forming the conically tapered film.

In known lubricating systems the radial holes in alignment with the lower bearing terminate the conically tapered film by providing a natural route through which the oil is inclined to pass thus preventing further flow up the axial bore and thereby starving the upper bearing of lubrication.

It is further known to provide a tilted bore in a shaft. That is, to arrange the bore at an angle to the central axis of the shaft. In such an arrangement, the surfaces of the bore are parallel and the upper radial hole is formed on the side of the bore that is in the direction of the tilt. In contrast, the lower radial hole is formed on the opposite side of the bore. The tilted bore has a disadvantage in that the positions of the upper radial hole and the lower radial hole are determined by the direction of the tilt and that the upper and lower holes are formed on opposite sides of the bore.

It is an aim of this invention to overcome these disadvantages.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, in a vacuum pump of the regenerative type or including a regenerative section in which a rotatable vertical shaft is supported by upper and lower bearings, a lubricating system for lubricating the bearings comprises an axial bore extending along the shaft and in communication with radial holes aligned respectively with the lower bearing and the upper bearing, the lower open end of the axial bore extending in to a shaft reservoir containing lubricating fluid, and in which the radial holes in alignment with the lower bearing are formed in a conically tapered surface of the axial bore.

According to another aspect of the present invention, a bearing lubrication system in a vacuum pump comprises a shaft having a bore along a longitudinal axis of the shaft, wherein a first length of the bore has a constant diameter and a second length of the bore has a decreasing diameter; an oil reservoir wherein the second length of the shaft is adapted to contact the oil reservoir; a lower hole in the second length of the shaft, the lower hole forming a lower fluid passage between the bore and the lower bearing; and an upper hole in the first length of the shaft, the upper hole forming an upper fluid passage between the bore and the upper bearing.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

An embodiment of the invention will now be described, by way of example, reference being made to the Figures of the accompanying drawings in which:

FIG. 1 is a cross section through a known compound vacuum pump including a regenerative section;

FIG. 2 is a detail of a known lubricating system illustrating how lubricating fluid establishes its own conical taper in a straight axial bore;

FIG. 3 is a detail similar to FIG. 2 but illustrating how in the known art excessive lubricating fluid can be delivered to the lower bearing whilst insufficient lubricating fluid is delivered to the upper bearing;

FIG. 4 is a detail similar to FIGS. 2 and 3 but illustrating an embodiment of the bearing lubricating system according to the present invention.

FIG. 5 is a detail similar to FIG. 1 that illustrates another embodiment of the bearing lubrication system according to the present invention.

FIG. 6 is a detail similar to FIGS. 2 and 3 but illustrating a further embodiment of the bearing lubricating system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIG. 1, which illustrates a known compound vacuum pump comprising a regenerative section 1 and a molecular drag (Holweck) section 2. The pump includes a casing 3 made from a number of different body parts bolted or otherwise fixed together and provided with relevant seals therebetween.

Mounted within the casing 3 is a vertical shaft 6 supported by an upper bearing 4 and a lower bearing 5. The shaft 6 is rotatable about its longitudinal axis and is driven by an electric motor 7 surrounding the shaft 6. Securely attached to the shaft for rotation therewith is a rotor 9. An axial bore 8 extends along a substantial length of the shaft and communicates with radial oil holes 8′ located near each bearing such that the radial oil holes 8′ are capable of delivering lubricating fluid to the upper and lower bearings.

Referring now to FIG. 2, it is known that a lubricating fluid such as oil establishes its own taper in a straight axial bore (as described in detail above) provided that a small ledge is available at the bottom (as shown) end of the axial bore.

Referring now to FIG. 3, it is known to provide two sets of radial holes 14, 12 which communicate at one end with the axial bore 18 of a rotatable shaft 16 and at the other end with respective upper and lower bearings (not shown). When the shaft 16 rotates, centrifugal force will force lubricating fluid from a reservoir through an open lower end of the shaft 16 and along the inside surface of the axial bore in the form of a thin film. However, the lower radial holes 12 effectively finalize the taper of the lubricating fluid film and prevent further flow of the film up the axial bore thereby starving the upper bearing of lubrication.

According to one embodiment of the present invention and with reference to FIG. 4 the bearing lubrication system of the present invention includes a vertical shaft 40 supported by upper bearings 42 and by lower bearings 44. The upper and lower bearings 42, 44 require lubrication during operation. To achieve such lubrication of the bearings 42, 44, the bearing lubrication system further includes a central axial bore 46 within the shaft 40 wherein the axial bore 46 is positioned along the longitudinal axis 48 of the shaft 40.

The bore 46 includes a lower portion or length along which the diameter of the bore 46 decreases or conically tapers toward an oil reservoir 49 that contacts the lower end of the bore 46. The bore 46 further includes an upper portion along which the diameter of the bore 46 is constant or straight.

To supply the lower bearings 44 with lubricating fluid, lower radial holes 41 in alignment with the lower bearings 44 are formed in the conically tapered portion of the axial bore 46. Notably, the lower radial holes 41 do not need to be in the same plane as the lower bearings 44, but should be located proximate to the lower bearings 44 in order to feed lubricant to the lower bearings 44. The lower radial holes 41 form lower fluid passages between the bore 46 and the lower bearings 44. Upper radial holes 43 located proximate to the upper bearings 42 can be formed in the straight portion of the bore 46 in order to feed lubricant to the upper bearings 42. The upper radial holes 43 form upper fluid passages between the bore 46 and the upper bearings 42. The embodiment shown in FIG. 4 shows the upper radial holes 42 and the lower radial holes 44 on opposite sides of the bore 46. However, the invention can also be practiced by positioning several lower radial holes 44 at several circumferential points around the conically tapered portion of the bore 46, and the lower radial holes 44 do not need to be positioned opposite to each other. Similarly, several upper radial holes 42 can also be positioned at several circumferential points around the bore 46 and do not need to be positioned opposite to each other.

When the shaft 40 rotates, centrifugal force causes lubricating fluid to flow from the oil reservoir 49 and up the walls of the conical taper of the axial bore in the form of a thin film. Forming a conical taper in the bore's 46 lower portion causes the bore's 46 surfaces to be at an angle to the longitudinal axis 48. As a result and in contrast to film formation in a bore having parallel surfaces as described above, the lubricant droplets in a conically tapered bore 46 experience a net resultant force in the direction away from the oil reservoir 49. That is, the droplets experience a component of force acting in the “upward” direction that overcomes the gravitational influence. This resultant force is governed by the speed at which the shaft is rotated coupled with the angle of the taper of the surface. Consequently, a film formed in the conically tapered bore 46 of the present invention will have a more uniform thickness than a film formed in a parallel bore as described in detail above.

Depending on the vector force experienced by these droplets, some droplets will pass into the lower radial holes 41 and into lubricate the lower bearings and other droplets will pass over the lower radial holes 41 to the upper radial holes 43 to lubricate the upper bearings. In other words, the mechanical conical taper of the axial bore 46 enables the lubricating fluid to flow both through the lower radial holes 41 to the lower bearings 44 and also past the lower radial holes 41 to the upper radial holes 43 to the upper bearings 42. The ratio of lubricating fluid leaving the respective holes is dependent upon oil jet hole diameter, taper angle, hole height within the conical taper and taper diameter.

According to another embodiment of the present invention and with reference to FIG. 5, the bearing lubrication system of the present invention is included in a vacuum pump 50 of the regenerative type or having a regenerative section 51. The vacuum pump 50 further includes a rotor 52 securely attached to a vertical shaft 54 wherein a motor 56 simultaneously rotates the rotor 52 and the shaft 54 about a longitudinal axis of the shaft. A casing 53 encloses the vacuum pump.

The bearing lubrication system in the vacuum pump 50 includes an axial bore 58 formed in the central axis of the shaft 54. The diameter of an upper portion or length of the bore 58 is constant whereas the diameter of a lower portion or length of the bore 58 conically tapers or decreases as a function of length. The tip of the conical taper contacts an oil reservoir (not shown) which supplies lubricating fluid to the bore 58.

The bearing lubrication system of vacuum pump 50 further includes upper bearings 62 and lower bearings 64. Upper radial holes 66 in the upper portion of the bore 58 are positioned near the upper bearings 62 and form an upper fluid passage between the bore 58 and the upper bearings 62 in order to lubricate the upper bearings 62. Similarly, lower radial holes 68 in the lower portion of the bore 58 are formed in the conical taper of the bore 58 and located proximate to the lower bearings 64. The lower radial holes 68 form a lower fluid passage between the bore 58 and the lower bearings 64 in order to lubricate the lower bearings 64. When the shaft 54 rotates, oil from the oil reservoir is drawn up into the conical taper of the lower portion of the bore 58 and flows through the lower radial holes 68 into the lower bearings 64. However, in contrast to prior art systems, the upper bearings 62 are not starved of oil because the position of the lower radial holes 68 in the conical taper of the bore 58 enables oil to flow beyond the lower radial holes 68 and into the upper radial holes 66 to lubricate the upper bearings 62.

According to yet another embodiment of the present invention and with reference to FIG. 6, the bearing lubrication system of the present invention includes a shaft 70 supported by upper and lower bearings (not shown). The upper and lower bearings require lubrication during operation of the system. The shaft 70 includes an axial bore 72 along a longitudinal axis 74 of the shaft 70. An upper portion of the axial bore 72 has a constant diameter and a lower portion of the axial bore 72 has a decreasing diameter or conical taper in a direction toward an oil reservoir 79 located at the bottom of the shaft 70. The lower portion of the axial bore 72 forms a conical taper that contacts the oil reservoir 79. An upper radial hole 76 is located in the upper portion of the bore 72 and supplies lubricating fluid to the upper bearing (not shown). A plurality of lower radial holes 78 are located in the conical taper in the lower portion of the axial bore 72 and supply lubricating fluid to the lower bearing (not shown). The lower radial holes may be of equal size and located in close proximity to each other. The lower radial holes 78 enable lubricating fluid to flow both into and past the lower radial holes 78 to ensure lubricating fluid reaches the upper radial hole 76 and the upper bearing. Notably, the upper radial hole 76 is located proximate to the upper bearing and the lower radial holes 78 are located proximate to the lower bearing.

While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the true spirit and scope of the present invention. 

1. In a vacuum pump of the regenerative type or including a regenerative section in which a rotatable substantially vertical shaft is supported by upper and lower bearings, a lubricating system for lubricating the bearings comprising an axial bore extending along the shaft and in communication with radial holes aligned respectively with the lower bearing and the upper bearing, the lower open end of the axial bore extending in to a shaft reservoir containing the lubricating fluid, and in which the radial holes in alignment with the lower bearing are formed in a conically tapered surface of the axial bore.
 2. In a vacuum pump of the regenerative type or including a regenerative section in which a rotatable substantially vertical shaft is supported by upper and lower bearings, a lubricating system for lubricating the bearings comprising an axial bore extending along the shaft and in communication with radial holes aligned respectively with the lower bearing and the upper bearing, the lower open end of the axial bore extending in to a shaft reservoir containing lubricating fluid, and in which the radial holes in alignment with the lower bearing are formed in a conically tapered surface of the axial bore and the lower bearings.
 3. A bearing lubrication system in a vacuum pump comprising: a shaft having a bore along a longitudinal axis of the shaft, wherein a first length of the bore has a constant diameter and a second length of the bore has a decreasing diameter; an oil reservoir wherein the second length of the shaft is adapted to contact the oil reservoir; a lower radial hole in the second length of the shaft, the lower radial hole forming a lower fluid passage between the bore and the lower bearing; and an upper radial hole in the first length of the shaft, the upper radial hole forming an upper fluid passage between the bore and the upper bearing.
 4. The bearing lubrication system of claim 3 wherein the vacuum pump comprises a rotor mounted on the shaft.
 5. The bearing lubrication system of claim 3 wherein the vacuum pump comprises a motor.
 6. The bearing lubrication system of claim 5 wherein the motor is adapted to simultaneously rotate the rotor and the shaft.
 7. The bearing lubrication system of claim 3 wherein the vacuum pump is of a regenerative type.
 8. A bearing lubrication system in a vacuum pump comprising: a shaft having a longitudinal axis and a bore, wherein the bore extends along a length of the shaft and forms a conical taper at a lower end of the shaft; a motor for rotating the shaft about the longitudinal axis; a plurality of upper bearings and a plurality of lower bearings wherein the upper bearings and the lower bearings support the shaft; an oil reservoir, wherein the lower end of the shaft is adapted to contact the oil reservoir so that when the shaft rotates oil flows up through the bore; a lower radial hole formed in the shaft and in the conical taper, wherein the lower radial hole is located proximate to at least one of the lower bearings; and an upper radial hole formed in the shaft and the bore, wherein the upper radial hole is located proximate to at least one of the upper bearings.
 9. The bearing lubrication system as claimed in claim 8 further comprising a rotor mounted on the shaft.
 10. The bearing lubrication system as claimed in claim 9 further comprising a stator surrounding the rotor and the shaft.
 11. The bearing lubrication system as claimed in claim 8 wherein the vacuum pump is of a regenerative type.
 12. A bearing lubrication system in a vacuum pump, the bearing lubrication system comprising: a shaft comprising a bore having a constant diameter along a first length of the shaft and a decreasing diameter along a second length of the shaft; an oil reservoir, wherein a portion of the second length of the shaft is adapted to contact the oil reservoir; a plurality of lower bearings and a plurality of upper bearings wherein the lower bearings and the upper bearings support the shaft; a plurality of lower radial holes in the shaft and the bore, wherein the lower radial holes are located proximate to the lower bearings; and a plurality of upper radial holes in the shaft and the bore, wherein the upper radial holes are located proximate to the upper bearings.
 13. The bearing lubrication system as claimed in claim 12 wherein the vacuum pump comprises a motor for rotating the shaft about a longitudinal axis of the shaft.
 14. The bearing lubrication system as claimed in claim 13 wherein the vacuum pump further comprises a rotor mounted on the shaft for rotation therewith.
 15. The vacuum pump as claimed in claim 14 wherein the vacuum pump further comprises a stator surrounding the rotor and the shaft.
 16. The bearing lubrication system as claimed in claim 14 wherein the vacuum pump is of a regenerative type. 